fix(arborist): ensure indentation is preserved (#4218)

It turns out that `new Arborist().buildIdealTree().meta.toString()` does
not take into account the indentation in the package.json (tabs, in my
case) the way `npm install --package-lock-only` does.

This fixes that. Also included a bonus commit that removes redundant
Promise stuff inside an `async function`.

2 files changed, 16 insertions, 12 deletions

diff --git a/workspaces/arborist/lib/arborist/build-ideal-tree.js b/workspaces/arborist/lib/arborist/build-ideal-tree.js
index 899d92ca9..dffcd546b 100644
--- a/workspaces/arborist/lib/arborist/build-ideal-tree.js
+++ b/workspaces/arborist/lib/arborist/build-ideal-tree.js
@@ -176,7 +176,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
   // public method
   async buildIdealTree (options = {}) {
     if (this.idealTree) {
-      return Promise.resolve(this.idealTree)
+      return this.idealTree
     }
 
     // allow the user to set reify options on the ctor as well.
@@ -194,8 +194,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
     process.emit('time', 'idealTree')
 
     if (!options.add && !options.rm && !options.update && this[_global]) {
-      const er = new Error('global requires add, rm, or update option')
-      return Promise.reject(er)
+      throw new Error('global requires add, rm, or update option')
     }
 
     // first get the virtual tree, if possible.  If there's a lockfile, then
@@ -334,6 +333,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
             root.meta.lockfileVersion = defaultLockfileVersion
           }
         }
+        root.meta.inferFormattingOptions(root.package)
         return root
       })
 
diff --git a/workspaces/arborist/lib/shrinkwrap.js b/workspaces/arborist/lib/shrinkwrap.js
index a7a68c98c..b45fea0ac 100644
--- a/workspaces/arborist/lib/shrinkwrap.js
+++ b/workspaces/arborist/lib/shrinkwrap.js
@@ -424,6 +424,18 @@ class Shrinkwrap {
       .map(fn => fn && maybeStatFile(fn)))
   }
 
+  inferFormattingOptions (packageJSONData) {
+    // don't use detect-indent, just pick the first line.
+    // if the file starts with {" then we have an indent of '', ie, none
+    // which will default to 2 at save time.
+    const {
+      [Symbol.for('indent')]: indent,
+      [Symbol.for('newline')]: newline,
+    } = packageJSONData
+    this.indent = indent !== undefined ? indent : this.indent
+    this.newline = newline !== undefined ? newline : this.newline
+  }
+
   load () {
     // we don't need to load package-lock.json except for top of tree nodes,
     // only npm-shrinkwrap.json.
@@ -451,15 +463,7 @@ class Shrinkwrap {
 
       return data ? parseJSON(data) : {}
     }).then(async data => {
-      // don't use detect-indent, just pick the first line.
-      // if the file starts with {" then we have an indent of '', ie, none
-      // which will default to 2 at save time.
-      const {
-        [Symbol.for('indent')]: indent,
-        [Symbol.for('newline')]: newline,
-      } = data
-      this.indent = indent !== undefined ? indent : this.indent
-      this.newline = newline !== undefined ? newline : this.newline
+      this.inferFormattingOptions(data)
 
       if (!this.hiddenLockfile || !data.packages) {
         return data